Photonic crystals are periodic optical (nano) structures in which optical mediums or materials having different refractive indexes are alternately arranged with periodicity that is second to the wavelength of light, the photonic crystals having a lattice period that is similar to the wavelength of light.
Such photonic crystals have a structure in which a portion between periodically and regularly-arranged particles is filled with the air. Colour of photonic crystals may be changed by adjusting the wavelength of reflected light by filling other materials instead of the air.
Examples of such photonic crystal structures include Coleoptera and Morpho butterfly.
When Coleoptera is with flaps of the wings in nature, blue colour flashes even in a dark forest. However, there is no colour pigment in the wings of Coleoptera. Blue colour is emitted by reflecting light having a predetermined wavelength and absorbing other lights due to a unique structure of the surface of the wings of Coleoptera. In this way, a phenomenon that colour is generated even without colour pigment is referred to as a structure colour.
FIG. 1 illustrates surface states of conventional photonic structures in which a Morpho butterfly found in South America, tail feathers of a peacock, a raw ore of opal, and the shell of an ormer that exist in the natural world and represent structure colour due to photonic structures, are enlarged by using an electronic microscope.
Blue colour is represented in the wings of the Morpho butterfly when the surface structure of the wings reflects blue light having a predetermined wavelength. The colour of the Morpho butterfly is dark like the body or edges of the wings. Such structure is found even in the feathers of some kinds of birds such as buprestid, wood chat, and peacock. A multilayered photonic crystal structure in which small air bags are regularly stacked in the wings or feathers can be observed by using the electronic microscope. In addition, the surface of leaves of Selaginella which is a fern, has a multilayered photonic crystal structure.
A three dimensional structure of such photonic crystals is used to represent beautiful colours and simultaneously, has a very good characteristic for adjusting the flow of light. Thus, a method of producing the structure in industry is required.
FIG. 2 is a cross-sectional view of a conventional structure colour of photonic crystals that exist in the wings of a Morpho butterfly.
As illustrated in FIG. 2, the conventional structure colour of photonic crystals that exist in the wings of the Morpho butterfly, is a structure in which a plurality of bases 101 that are arranged vertically and a plurality of protrusions 102 that are arranged to be asymmetrical to side surfaces of the bases 101, are formed as one body.
The conventional structure colour of photonic crystals may represent similar colour to that of Morpho butterfly, etc. However, shape structures of the conventional structure colour of photonic crystals and Morpho butterfly are asymmetrical. Thus, it is not easy to use an imprint processing method in the conventional structure colour of photonic crystals, and mass production is not possible.